1. Field of the Invention
In general, the present invention relates to axle differentials, such as those used as part of the drive train on automobiles. More particularly, the present invention relates to differentials that contain active mechanisms to compensate for slip in at least one of the axles.
2. Prior Art Description
Most automobiles have engines and transmissions. The engine and transmission is used to turn a driveshaft. The driveshaft is connected to a differential. The differential transfers the rotational energy of the driveshaft to the axles and wheels of the automobile.
When an automobile is driving in a straight line, the wheels on the left side of the vehicle and the wheels on the right side of the vehicle rotate at the same speed. However, when the automobile makes a turn, the wheels on the outside of the turn must travel farther than the wheels on the inside of the turn. Consequently, the wheels on the outside of the turn must rotate at a slightly faster rate than the inside wheels during the turn. The use of differentials enables opposing axles on opposite sides of the vehicle to rotate at different speeds. As such, the wheels of the vehicle can each rotate at the proper speed to accommodate a turn.
Most prior art differentials are designed assuming that the wheels of the automobile will be encountering good road conditions. In real life, this is not always the case. Roads are often covered in snow, ice, dirt, gravel, mud and the like that can make a wheel skid slightly during a turn. In such situations, differentials may misinterpret the conditions and allow too much power to be applied to the slipping wheel. This can adversely affect the safety of the vehicle.
In attempts to limit such traction problems, some vehicle manufacturer's use limited-slip differentials. A limited-slip differential is a type of automotive differential gear arrangement that allows for some difference in angular velocity of the output shafts, but imposes mechanical boundaries on the disparity. In an automobile, such limited-slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity. In the prior art, there are many different types of limited slip differentials. However, the present invention relates generally to electronic limited slip differentials. In an electronic limited slip differential, sensors and various electromechanical components are used to automatically adjust the differential depending upon driving speed and traction conditions. Such prior art is exemplified by U.S. Pat. No. 7,357,748 to Kelly, entitled Limited Slip Differential.
Prior art electronic limited slip differentials have certain innate problems. Being limited slip differentials, such prior art differentials do allow for some slip of the axles and wheels, albeit that the slip is limited in range. Under certain circumstances, even limited slip can detract from the safety of a vehicle. Torque transfer is another common problem associated with limited slip differentials. Limited slip differentials endeavor to redirect torque to the axle with the most traction. However, some torque is always lost to the axle of the slipping wheel. Furthermore, differentials are traditionally mechanical devices. The addition of electronics to differentials has increased their complexity and corresponding cost of manufacture. The use of electronic controls within the differential makes the differential expensive to build and difficult to repair.
A need therefore exists for an improved differential system that precisely controlled at all times and allows for no significant slip in the controlled axles. A need also exists for a differential that has the precision of electronic controls, yet is simple and inexpensive to manufacture. These needs are met by the present invention as described and claimed below.